The apostle Paul affirms that the God the Israelites of the Old Testament knew—the One they looked to as their "Rock" of strength (see Deuteronomy 32:4; Psalm 18:2)—was the One we know as Jesus Christ. Notice what Paul wrote in 1 Corinthians 10:1-4: "All our fathers were under the cloud, all passed through the sea, all were baptized into Moses in the cloud and in the sea, all ate the same spiritual food, and all drank the same spiritual drink. For they drank of that spiritual Rock that followed them, and that Rock was Christ."
Jesus was the One who spoke to Moses and told Him to return to Egypt to bring the Israelites to freedom. Jesus was the LORD (YHWH) who caused the plagues to come on Egypt. He was the God who led the Israelites out of Egypt and through the wanderings for 40 years. He was the Lawgiver who gave the laws to Moses and spoke to Moses on a regular basis. He was the LORD who dealt with Israel throughout their national history.
Yes, astounding as it seems, Jesus Christ is the LORD (YHWH) spoken of so often in the Old Testament.